PROTOZOA IN OPEN RESERVOIRS

The impact of storage of potable water in open reservoirs was assessed by examining inlet and effluent water samples from six open finished water reservoirs used by four New Jersey utilities. Water quality para meters investigated included Giardia cysts, Cryptosporidium oocysts, t otal and fecal coliforms, bacteriophage, heterotrophic plate count bac teria, turbidity, particle counts, chlorine residuals and other parame ters. Fifteen percent of inlet samples and 25 percent of effluent samp les contained the organisms. When data for cysts and oocysts were comb ined, the difference in concentrations between the inlet and effluent was statistically significant, even when results were adjusted for ana lytical recovery efficiency. Although the concentration of protozoa in creased following open reservoir storage, the analytical method used d oes not permit assessment of the organisms' public health significance . Nearly all of the cysts and oocysts were empty or contained undiscer nible internal structures, suggesting the health risk is low. The impl ication of these findings for watershed control programs is discussed.